The magnetic properties of a 15uc thick LSMO thin film on SrTiO3 (STO) substrate atT=150K was investigated using the technique of ferromagnetic resonance (FMR). The FMRmeasurement of the 15uc thick LSMO thin film at a frequency f = 9.75GHz and powerP = 0.6325mW as a function of the angle between the static magnetic field H, and theeasy direction of magnetization within the sample plane in the "in-plane" (IP) configuration displayed an FMR spectrum. This resonance spectrum shows unequal resonance field peaks. The unequal peaks in the resonance field may be attributed to the uniaxial anisotropy field which satisfies the conditions for ferromagnetic resonance. The unequal peaks in the resonance field shows a maximum and minimum with negative and positive curvature which either increases or decreases with respect to the resonance field respectively. This increase or decrease in the resonance field depends on the magnetization direction. It has been shown that for a thick 15uc LSMO thin film at T = 150K the center position and the full width half maximum (FWHM) of the resonance field were 1070.1875 Oe and 159.3125 Oe respectively.